Evaporated fuel leaked from a fuel tank, a float chamber of a carburetor or other engine sections contains a substantial amount of hydrocarbons and is a cause of air pollution and fuel loss. Various types of technology to prevent evaporated fuel leakage are known. One of the representative technologies is a system in which evaporated fuel from a fuel tank is absorbed and stored in a canister by an absorbent such as activated carbon therein, and the evaporated fuel once absorbed and stored in this canister is purged and supplied to the engine when it runs.
Japanese Patent Laid Open Publication No. 130254-1990 discloses an evaporated fuel processing apparatus for a fuel tank in an engine comprising a communicating path which communicates a fuel tank to a canister, a relay valve which opens and closes this communicating path, a shut down detecting means for detecting when the engine is shut off or the vehicle is stopped, and a driving means for opening the relay valve for a specified period of time after detecting an engine shut down or stopping of the vehicle. The result is that evaporated fuel in the fuel tank is introduced into and collected in the canister which substantially reduces the quantity of evaporated fuel released into the atmosphere from a fuel tank inlet port when the filler cap is opened.
A conventional type of evaporated fuel controller is shown in FIG. 4. A path 132 communicates a surge tank 108 located downstream from a throttle valve 106 to a fuel tank 116. The throttle valve 106 is disposed within an air intake path 110 of an engine (not shown). A canister 134 in line with path 132 absorbs and stores evaporated fuel. The path 132 comprises a first path 136 communicating the fuel tank 116 to the canister 134 and a second path 138 communicating the canister 134 to the air intake path 110. A check valve 140 is provided in the first path 136 between the fuel tank 116 and the canister 134. Check valve 140 sets a pressure in the fuel tank 116 and the canister 134 to a specified level thereby controlling the quantity of evaporated fuel (HC) generated in the fuel tank 116. The pressure in the fuel tank is set to a level slightly higher than the atmospheric pressure so that the pressure in the fuel tank is maintained at a constant level (pressure accumulation).
A throttle sensor (not shown) for detecting an opening degree of the throttle valve 106 and a solenoid valve 144 in line with the second path 138 are each connected to a controller (not shown).
During refueling operations, when cap 116A of the fuel tank 116 is opened, internal pressure in the tank is released to the atmosphere and evaporated fuel in the fuel tank (HC) is released, which causes air pollution. Starting in 1995, the United States will impose restrictions over evaporated fuel which require that the pressure in a fuel tank while an engine is running be held below a specified level, for instance, 10 inch mmAg or less. Development of an evaporated fuel controller which can satisfy this restriction is strongly desired.
In order to solve the problems as described above, an evaporated fuel system according to the present invention is characterized in that an evaporated fuel path is formed with a first path communicating a fuel tank to a canister and a second path communicating a canister to an air intake path, a pressure control valve is provided in the first path, a first solenoid valve is provided in the second path, the canister communicates with the atmosphere via a second solenoid valve, a communicating path communicates the air intake path to a pressure chamber of the pressure control valve, a third solenoid valve is provided in the communicating path, a pressure sensor detects pressure in the fuel tank, and a control means communicates the fuel tank to the canister by opening the third solenoid valve which in turn opens the pressure control valve when any one of specified conditions for running the engine are not satisfied.
As constructed according to the present invention as described above, when any one of the specified conditions for running the engine are not satisfied, the controller provides controls to communicate the fuel tank with the canister by opening the third solenoid valve which opens the pressure control valve.